Circuit Description - Sharp QA-1650 Service Manual

CIRCUIT DESCRIPTION
1.GENERAL
Circuits will be described in reference to the QA1650 BLOCK DIAGRAM in Fig.2.
Composite video signal enters via pin jack connector, COMPOSITE VIDEO INPUT CIRCUIT, MODE
SELECTOR CIRCUIT,and A/D CONVERTER CIRCUIT,and are converted into digital RGB signals.
Analog RGB signals from IBM PS/2 or Apple MAC I enter via the provided cable, 26-pin connector the
COMPUTER ANALOG INPUT CIRCUIT, MODE SELECTOR CIRCUIT and A/D CONVERTER CIRCUIT
and are converted into digital RGB signals. Also QA1650 has EXTERNAL MONITOR OUTPUT CONNEC-
TOR, which outputs via COMPUTER ANALOG INPUT CIRCUIT these analog signals after amplifing.
Digital RGB video signals from IBM PC EGA or CGA enter via the provided cable and 26-pin connector
COMPUTER DIGITAL INPUT CIRCUIT.
MODE SELECTOR CIRCUIT selects either RGB signal or composite video signal by receiving control
signal from IC2(M.P.U.) via IC1. QA-1650 has automatic video recognition function. This is performed by
receiving and analyzing H and V sync. and A/D signal from CN3.
When analog RGB signal is chosen, each 8-bit data of RGB converted by A/D CONVERTER CIRCUIT is
sent to MODE SELECTOR CIRCUIT. When digital is chosen, data is sent to MODE SELECTOR directly.
They are written into FIELD MEMORY (IC3,4,and 5) in accordance with the timing of FWCK,WRS,OGW
which are generated from inputted Hsync, and Vsync in IC1. Since LCD control is asynchronous with the
RGB data, writtng data into FIELD MEMORY must be read out in accordance with LCD unit display
timing. For the reason, RGB data in the FIELD Memory are read out in accordance with the timing of read
out signals (FRCK,RRS,FUE) which generated from IC1. The video data read out from FIELD MEMORY
passes LINE BUFFER(IC8, 9, 10), inputted into IC1,corrected for color,and converted into LCD display
data(R0O~5,G0~5,B0~5).
QA1650 has display enlargement function. These functions are executed by LINE BUFFER(IC8, 9, 10).
IC2 (MPU) controls setting parameter in IC1 via key input on SWITCH P.W.B or REMOTE CONTROL
UNIT. Also IC2 controls EEPROM(IC15).Control data changed via key input are held in
EEPROM,remaining stored even after power is turned off.
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